Optical reader having reduced parameter determination delay

ABSTRACT

In the present invention, an optical reader image sensor is adapted to clock out image data from an image sensor according to “low resolution” mode of operation in order to reduce a parameter determination delay of the reader. In a low resolution mode, some pixels of the readers image sensor array are clock out at normal clock out speed sufficient to develop electrical signals accurately reflecting the intensity of light at the respective pixel positions, while other pixels of the array are either not clocked out or are clocked out at a higher clock out rate which may be insufficient to allow development of electrical signals that accurately represent light incident on the image sensor&#39;s sensor array but which nevertheless, results in a reduction of the overall frame clock out rate of the frame of image data. An optical reader according to the invention operates in a low resolution frame clock out mode to capture a low resolution parameter determining frame of image data at high speed, reads pixel data from the parameter determination frame to determine an operation parameter based on actual illumination conditions, then utilizes the operation parameter in operating an optical reader.

FIELD OF THE INVENTION

[0001] The present invention relates to optical readers in general andin particular to a method for reducing a parameter determination delayof an optical reader.

BACKGROUND OF THE PRIOR ART

[0002] Prior to commencing comprehensive image data processing, whichmay include e.g. searching for symbol or character representations,decoding and character recognition processing, presently availableoptical readers clock out and capture in a memory location at least oneexposure test frame of image data, read pixel data from thememory-stored exposure test frame to determine an exposure parametervalue that is based on actual illumination conditions, then utilize theexposure parameter value in the exposure of a frame of image data thatis clocked out, and then subjected to searching, decoding, and/orcharacter recognition processing. The frame of image data exposedutilizing the exposure parameter based on actual illumination conditionsis not available for reading until after it is clocked out. Presentlyavailable optical readers therefore exhibit an appreciable inherentexposure parameter determination delay. Readers having higher resolutionimagers have slower frame clock out rates and therefore longer exposureparameter determination delays.

[0003] There is a growing demand for higher resolution optical readers,including optical readers that incorporate mega pixel image sensors.Accordingly, there is growing need to address the parameterdetermination delay problem associated with presently available opticalreaders.

SUMMARY OF THE INVENTION

[0004] According to its major aspects and broadly stated, the presentinvention is a method for controlling an optical reader to reduce thereader's parameter determination delay. According to the invention, animage sensor is adapted to clock out image data from an image sensoraccording to two modes of operation, a “low resolution” clock out modeof operation and a “normal resolution” clock out mode of operation.

[0005] In a low resolution mode, some pixels of the reader's imagesensor pixel array are clocked out at a normal clock out speedsufficient to develop electrical signals that accurately represent theintensity of light incident on the pixel array, while other pixels ofthe array are either not clocked out or are clocked out at a higherclock out rate which is insufficient to allow development of electricalsignals that accurately represent the intensity of light at therespective pixels but which nevertheless, result in an increase in theoverall frame clock out rate of the frame of image data. In a normalresolution mode of operation the image sensor is caused to clock outelectrical signals corresponding to each pixel of the array at aconstant “normal mode” speed which is a speed sufficient to ensure thatthe electrical signal corresponding to each pixel accurately representsthe intensity of light incident on the pixel.

[0006] An optical reader according to the invention operates an imagesensor in a low resolution mode of operation in order to clock out andcapture a parameter-determining frame of image data at high speed, readspixel data from the parameter determination frame to determine anoperation parameter based on actual illumination conditions, thenutilizes the operation parameter in operating an image sensor accordingto high resolution mode in the clocking out of a succeeding frame ofimage data that is captured and subjected to comprehensive image dataprocessing which may include image data searching, decoding, and/orrecognition processing. Clocking out some of the pixels of an array athigh speed during execution of the low resolution mode significantlydecreases the reader's parameter determination delay.

[0007] These parameters determined by reading pixel values from a lowresolution parameter determination frame of image data according to theinvention may include an exposure time parameter, an amplificationparameter for controlling amplification of an electrical signal prior toits analog to digital conversion, an illumination level parameter(intensity or period of illumination), a dark or light level adjustmentparameter and an analog-to-digital converter reference voltage parameterfor adjusting the high and/or low reference voltages of the reader'sanalog to digital converter.

[0008] These and other details, advantages and benefits of the presentinvention will become apparent from the detailed description of thepreferred embodiment hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIGS. 1a and 1 b are image maps illustrating possible lowresolution frames of image data clock out during a low resolution frameclock out mode of the invention;

[0010]FIG. 2a is a block diagram of an optical reader of a type in whichthe invention may be incorporated;

[0011]FIGS. 2b-2 h show various types of optical reader housings inwhich the invention may be incorporated;

[0012]FIG. 3a is a process flow diagram illustrating frame clockingoperations in an optical reader having an image sensor including aone-frame buffer.

[0013]FIG. 3b is a time line illustrating frame clock out operations ina prior art optical reader;

[0014]FIG. 3c is a time line illustrating a frame clock out ofoperations in an optical reader operated according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] When operated to generate valid pixel data, presently availableoptical reading devices clock out electrical signals corresponding topixel positions of an image sensor at a uniform clock out rate such thatthe electrical signal corresponding to each pixel of the image sensorarray accurately represents light incident on the pixel.

[0016] By contrast, an image sensor of the present invention is made tooperate under two major frame capture modes, a “low resolution” frameclock out mode and a “normal resolution” frame clock out mode. In a “lowresolution” mode of operation, an image sensor according to theinvention is operated to clock out electrical signals corresponding tosome pixels of an image sensor array at a high clock out rate and otherpixels of the image sensor at a normal clock out rate. Clocking out aportion of the electrical signals using a faster than normal clock outrate results in a reduction in the overall frame clock out time whileclocking out a portion of the signals at a normal clock out rate enablesthe generation of pixel data sufficient to enable determination ofparameter settings for use in subsequent frame captures. In a “normalresolution” mode of operation the image sensor is operated to clock outelectrical signals corresponding to pixels of the array using a singleuniform clock out speed as in prior art readers. The low resolution modeof operation may also be carried out by clocking out electrical signalscorresponding to only a portion of a frame's pixels and not clocking outelectrical signals corresponding to the remaining pixels.

[0017] A reader configured in accordance with the invention clocks outand captures in a memory storage location at least one parameterdetermination frame of image data in a “low resolution” frame capturemode, reads pixels of the parameter determination frame in establishingat least one operation parameter that is based on actual illuminationconditions, utilizes the determined operation parameter in clocking outa subsequent frame of image data in a “normal resolution mode,” thencaptures and subjects the frame of image data clocked out utilizing theoperation parameter to image data searching, decoding, and/orrecognition processing.

[0018] An optical reading system is which the invention may be employedis described with reference to the block diagram of FIG. 2a.

[0019] Optical reader 10 includes an illumination assembly 20 forilluminating a target object T, such as a 1D or 2D bar code symbol, andan imaging assembly 30 for receiving an image of object T and generatingan electrical output signal indicative of the data optically encodedtherein. Illumination assembly 20 may, for example, include anillumination source assembly 22, together with an illuminating opticsassembly 24, such as one or more lenses, diffusers, wedges, reflectorsor a combination of such elements, for directing light from light source22 in the direction of a target object T. Illumination assembly 20 maycomprise, for example, laser or light emitting diodes (LEDs) such aswhite LEDs or red LEDs. Illumination assembly 20 may include targetillumination and optics for projecting an aiming pattern 27 on target T.Illumination assembly 20 may be eliminated if ambient light levels arecertain to be high enough to allow high quality images of object T to betaken. Imaging assembly 30 may include an image sensor 32, such as a 1Dor 2D CCD, CMOS, NMOS, PMOS, CID OR CMD solid state image sensor,together with an imaging optics assembly 34 for receiving and focusingan image of object T onto image sensor 32. The array-based imagingassembly shown in FIG. 2a may be replaced by a laser array based imagingassembly comprising multiple laser sources, a scanning mechanism, emitand receive optics, at least one photodetector and accompanying signalprocessing circuitry.

[0020] Optical reader 10 of FIG. 2a also includes programmable controlcircuit 40 which preferably comprises an integrated circuitmicroprocessor 42 and an application specific integrated circuit (ASIC44). The function of ASIC 44 could also be provided by field programablegate array (FPGA). Processor 42 and ASIC 44 are both programmablecontrol devices which are able to receive, output and process data inaccordance with a stored program stored in memory unit 45 which maycomprise such memory elements as a read/write random access memory orRAM 46 and an erasable read only memory or EROM 47. RAM 46 typicallyincludes at least one volatile memory device but may include one or morelong term non-volatile memory devices. Processor 42 and ASIC 44 are alsoboth connected to a common bus 48 through which program data and workingdata, including address data, may be received and transmitted in eitherdirection to any circuitry that is also connected thereto. Processor 42and ASIC 44 differ from one another, however, in how they are made andhow they are used.

[0021] More particularly, processor 42 is preferably a general purpose,off-the-shelf VLSI integrated circuit microprocessor which has overallcontrol of the circuitry of FIG. 2a, but which devotes most of its timeto decoding image data stored in RAM 46 in accordance with program datastored in EROM 47. Processor 44, on the other hand, is preferably aspecial purpose VLSI integrated circuit, such as a programmable logic orgate array, which is programmed to devote its time to functions otherthan decoding image data, and thereby relieve processor 42 from theburden of performing these functions.

[0022] The actual division of labor between processors 42 and 44 willnaturally depend on the type of off-the-shelf microprocessors that areavailable, the type of image sensor which is used, the rate at whichimage data is output by imaging assembly 30, etc. There is nothing inprinciple, however, that requires that any particular division of laborbe made between processors 42 and 44, or even that such a division bemade at all. This is because special purpose processor 44 may beeliminated entirely if general purpose processor 42 is fast enough andpowerful enough to perform all of the functions contemplated by thepresent invention. It will, therefore, be understood that neither thenumber of processors used, nor the division of labor there between, isof any fundamental significance for purposes of the present invention.

[0023] With processor architectures of the type shown in FIG. 2a, atypical division of labor between processors 42 and 44 will be asfollows. Processor 42 is preferably devoted primarily to such tasks asdecoding image data, once such data has been stored in RAM 46,recognizing characters represented in stored image data according to anoptical character recognition (OCR) scheme, handling menuing options andreprogramming functions, processing commands and data received fromcontrol/data input unit 39 which may comprise such elements as trigger74 and keyboard 78 and providing overall system level coordination.

[0024] Processor 44 is preferably devoted primarily to controlling theimage acquisition process, the A/D conversion process and the storage ofimage data, including the ability to access memories 46 and 47 via a DMAchannel. Processor 44 may also perform many timing and communicationoperations. Processor 44 may, for example, control the illumination ofLEDs 22, the timing of image sensor 32 and an analog-to-digital (A/D)converter 36, the transmission and reception of data to and from aprocessor external to reader 10, through an RS-232, a network such as anethernet, a serial bus such as USB, a wireless communication link (orother) compatible I/O interface 37. Processor 44 may also control theoutputting of user perceptible data via an output device 38, such as abeeper, a good read LED and/or a display monitor which may be providedby a liquid crystal display such as display 82. Control of output,display and I/O functions may also be shared between processors 42 and44, as suggested by bus driver I/O and output/display devices 37′ and38′ or may be duplicated, as suggested by microprocessor serial I/Oports 42A and 42B and I/O and display devices 37″ and 38′. As explainedearlier, the specifics of this division of labor is of no significanceto the present invention.

[0025]FIGS. 2b through 2 g show examples of types of housings in whichthe present invention may be incorporated. FIGS. 2b-2 g show 1D/2Doptical readers 10-1, 10-2 and 10-3. Housing 12 of each of the opticalreaders 10-1 through 10-3 is adapted to be graspable by a human hand andhas incorporated therein at least one trigger switch 74 for activatingimage capture and decoding and/or image capture and characterrecognition operations. Readers 10-1 and 10-2 include hard-wiredcommunication links 79 for communication with external devices such asother data collection devices or a host processor, while reader 10-3includes an antenna 80 for providing wireless communication device or ahost processor.

[0026] In addition to the above elements, readers 10-2 and 10-3 eachinclude a display 82 for displaying information to a user and a keyboard78 for enabling a user to input commands and data into the reader.

[0027] Any one of the readers described with reference to FIGS. 2bthrough 2 g may be mounted in a stationary position as is illustrated inFIG. 2h showing a generic optical reader 10 docked in a scan stand 90.Scan stand 90 adapts portable optical reader 10 for presentation modescanning. In a presentation mode, reader 10 is held in a stationaryposition and an indicia bearing article is moved across the field ofview of reader 10.

[0028] As will become clear from the ensuing description, the inventionneed not be incorporated in a portable optical reader. The invention mayalso be incorporated, for example, in association with a control circuitfor controlling a non-portable fixed mount imaging assembly thatcaptures image data representing image information formed on articlestransported by an assembly line, or manually transported across acheckout counter at a retail point of sale location. Further, inportable embodiments of the invention, the reader need not be hand held.The reader may be part or wholly hand worn, finger worn, waist worn orhead worn for example.

[0029] Referring again to particular aspects of the invention, a lowresolution frame clock out mode of the invention is described in detailwith reference to the pixel maps of FIGS. 1a and 1 b. Control circuit 40establishes a clock out rate for clocking out an electrical signalcorresponding to a pixel of an image sensor 32 by appropriate statecontrol of control signals in communication with image sensor 32. In thepresent invention, image sensor 32 is selected to be of a type whosepixel clock out rate can be varied by way of control signals receivedfrom control circuit 40. In presently available optical readers, animage sensor's pixel clock out rate is not changed during the course ofclocking out of a frame of image data.

[0030] In a “low resolution” frame clock out mode of the invention,however, control circuit 40 causes image sensor 32 to clock outelectrical signals corresponding to the pixels of the array at least twospeeds during a single frame capture period. During a single frame clockout period, control circuit 40 controls image sensor 32 so that somepixels are clocked out at normal clock out rate sufficient to developelectrical signals accurately representing the intensity of light at therespective pixel positions, while other pixels are either not clockedout or are clocked out at a clock out rate which may be insufficient toallow development of electrical signals that accurately represent theintensity of light at the respective pixels but which neverthelessresults in a reduction of the overall frame clock out time of the frameof image data being clocked out.

[0031]FIG. 1a shows a schematic diagram of an exemplary image map framethat is clocked out according to the low resolution frame clock out modeof the invention and then captured into memory 45. The image map isdivided into “zones” of valid data and invalid data. Valid zones 84shown are rows of pixels that are clocked out at a normal clock outspeed while invalid zones 86 shown are rows of pixel that are clockedout at a faster clock out speed, which is normally (but not necessarily)a speed insufficient to allow development of electrical signalsaccurately representing the intensity of light at a pixel.

[0032]FIG. 1b shows another possible division of an image map into validzones and invalid zones. This type of embodiment in which valid zones 84comprise less than full pixel rows is conveniently realized byappropriate control of an image sensor manufactured using CMOSfabrication methods. Using CMOS fabrication methods, an image sensor canbe merged with a microprocessor, an ASIC, or another timing device on asingle die to the end that a preestablished clocking sequence in which apixel clock out rate is changed multiple times during the course ofclock out a frame of image data may be actuated in response to theactivation of a single control signal in communication with image sensor32.

[0033] Using CMOS fabrication techniques, image sensors are readily madeso that electrical signals corresponding to certain pixels of a sensorcan be selectively clocked out without clocking out electrical signalscorresponding to remaining pixels of the sensor. CMOS image sensors areavailable from such manufacturers as Symagery, Pixel Cam, Omni Vision,Sharp, Natural Semiconductor, Toshiba, Hewlett-Packard and Mitsubishi.Further aspects of a partial frame clock out mode are described incommonly assigned application Serial No. ______ entitled “Optical ReaderHaving Partial Frame Operating Mode” filed concurrently herewith andincorporated herein by reference.

[0034] The invention is also conveniently realized with use of an imagesensor having an image sensor discharge function. Image sensors having adischarge function are typically adapted to receive a discharge clockout signal which when active results in all pixels of a frame being readout at a high clock out rate insufficient to allow development ofelectrical signals. In presently available readers having a directionalfunction, a control circuit sets the discharge clocking signal to anactive state while clocking out an initial “discharge period” frame ofimage data immediately after reception of a trigger actuation. Thisinitial discharge process removes any residual charges built up on imagesensor 32 prior to capturing a first frame including valid pixel data.

[0035] For producing an image map divided into valid and invalid zonesusing an image sensor having a discharge function, control circuit 40may be made to intermittently change the state of a discharge clock outsignal during a frame clock out period during which image sensor 32 isotherwise operated according to a normal resolution clock out mode.

[0036] An exemplary embodiment of the invention in which the inventionis employed in a reader equipped with a SONY ICX084AL CCD image sensor(that includes a one frame analog buffer memory) and a SONY CXD2434TQtiming generator is described with reference to FIGS. 3a, 3 b and 3 c.FIG. 3a shows a flow diagram, of an imaging system in which the imagesensor includes a one frame buffer memory. For purposes of illustratingthe advantages of the invention, FIG. 3b shows a time line illustratingthe time required to clock out and capture a frame of image data usefulfor searching and decoding in a prior art reader having a buffer memorynot configured to operate in accordance with a low resolution frameclock out mode. FIG. 3c shows a time line illustrating the time requiredto clock out and capture a frame of image data useful for searching,decoding, and recognizing characters in a reader having a buffer memoryconfigured to operate in a low resolution frame clock out mode accordingto the invention.

[0037] When a reader includes a one frame buffer memory, then theactivation of an appropriate frame clock out signal by image sensor 32causes electrical charges representative of light on pixels of an imagesensor's pixel array 32 a to be transferred to analog buffer memory 32 band causes electrical signals corresponding to pixel value storagelocations of buffer 32 b (representing light on the pixels during aprevious timing period) to be clocked out to analog to digital converter36 so that the frame of image data stored on buffer memory can becaptured in memory 45, wherein the data may be read by control circuit40.

[0038] Referring to time line 92 corresponding a prior art reader it canbe seen that a substantial parameter determination delay is presentwithout use of a low resolution frame capture mode according to theinvention. At time T0, control circuit 40 activates a frame dischargecontrol signal so that residual charges built up in the storagelocations of buffer memory 32 b are eliminated or “cleaned” during clockout period CPO.

[0039] At time T1, control circuit 40 activates a frame clocking signalto commence the clock out a first frame of pixel data according to anormal resolution frame clock out mode(the pixel data clocked out duringclock out period CP1 is normally invalid pixel data). During clock outperiod CP1, the charges built up on pixel array 32 a during clock outperiod CP0 are transferred to buffer memory 32 b and then clocked out toA/D converter 36. Also during clock out period CP1 pixel array 32 a isexposed to light for a time determined by an exposure parameter value,e₀, that was previously transmitted at time Te₀. prior to time T1. Theexposure parameter e₀ is based on previous exposure values during aprevious trigger actuation period or based on expected illuminationconditions, but is not based on actual illumination conditions present.

[0040] At time T2, control circuit 40 activates a frame clock out signalto commence the clock out of a second frame of image data in accordancewith a normal resolution frame clock out mode. During clock out periodCP2, the charges built up on pixel array 32 a during clock out periodCP1 are transferred to buffer memory 32 b and then clocked out to A/Dconverter 36. Also during clock out period CP2 pixel array 32 is exposedto light for a time determined by an exposure parameter value, e₁, thatwas previously transmitted at time Te₁ prior to time T2. The exposureparameter e₁, like exposure parameter e₀, also cannot be based on actualillumination conditions since the most recent frame image data availablefor reading by circuit 40 prior to the transmittal of exposure parametere₁ is the invalid frame data resulting from transmittal of framedischarge signal at time T0.

[0041] At time T3, control circuit 40 activates a frame clock out signalto commence the capture of a third frame of image data in accordancewith a normal resolution frame clock out mode. During clock out periodCP3, the charges built up on pixel array 32 a during clock out periodCP2 are transferred to buffer memory 32 b and then clocked out to A/Dconverter 36. Also during clock out period CP3, pixel array 32 a isexposed to light for a time determined by an exposure parameter value,e₂, that was previously transmitted at time Te₂ prior to time T3. Unlikethe previous exposure values e₀ and e₁, the exposure parameter value e₂can be a value determined from actual illumination conditions since theframe of image data resulting from pixel array 32 a being exposed tolight during clock out period CP1, is available for reading by controlcircuit 40 prior to the time that the exposure parameter e₂ must becommunicated to image sensor 32. However, because of the built in oneframe delay resulting from the presence of buffer 32 b, it is seen thata frame of image data clocked out while being exposed with the exposureparameter value e₂, determined based on actual illumination conditions,will not be available for reading by control circuit unit after theexpiration of clocking period CP4. Accordingly, it can be seen that theabove reader exhibits a typical parameter determination delay of fournormal resolution clock out periods, CP1+CP2+CP3+CP4 plus the framedischarge clock out parameter CP0. The normal resolution frame clock outrate of the above-referenced SONY image sensor is about 33.37 ms and theframe discharge rate is about 8.33 ms, resulting in a typical-case totalparameter determination delay in the example described of 140 ms (anearlier frame may be subjected to image data searching, decoding, andrecognition if e₀ or e₁ yields an image of acceptable quality).

[0042] Advantages of operating image sensor 32 according to a lowresolution frame clock out mode of operation are easily observable withreference to time line 94 corresponding to a reader having an imagesensor operated in accordance with a low resolution frame clock outmode. In the example illustrated by time line 94 control circuit 40operates image sensor as described in connection with FIG. 3b exceptthat control circuit 40 operates image sensor 32 according to a lowresolution frame clock out mode during clocking periods CP1, CP2, andCP3. Because electrical signals corresponding to only some of the pixelsduring these timing periods are clocked out at speeds sufficiently slowto read valid image data, the total frame clock out time associationwith these clocking periods is significantly shorter than that of aframe clocked out according to a normal resolution frame clock out mode.In an exemplary embodiment in which control circuit 40 alternatinglychanges the state of a discharge clock out control signal (known as anEFS signal) in communication with a SONY ICX084AL CCD image sensor, toresult in a zone division pattern having valid zones comprising fourpixel rows clocked out at normal speed bounded by invalid rows havingeighteen rows of pixels clock out at high speed, the low resolutionframe clock out rate is 8.52 ms. The overall typical parameterdetermination delay is therefore reduced to T0+T1+T2+T3+T4=66.2 ms ascompared to the 140 ms delay in the prior art reader example describedwith reference to FIG. 3a.

[0043] In the example described in which image sensor 32 comprises a oneframe buffer 32 b, pixel array 32 a is exposed to light for at leastsome time currently as electrical signals are clocked out from buffer 32b. In the control of presently available image sensors that do not haveone frame buffers, frame clock out periods normally follow frameexposure periods without overlapping the exposure periods.

[0044] A low resolution parameter determination frame of image dataclocked out using a low resolution clock out mode is useful fordetermining an exposure control parameter because exposure parametervalues can be accurately determined by sampling only a small percentageof pixel values from a frame of image data. In fact, for improving theprocessing speed of an optical reader it is preferred to determine anexposure control value based on a sampling of a small percentage ofpixel values from a frame of image data. The proper exposure parametersetting varies substantially linearly with illumination conditions, andtherefore is readily determined based on a sampling of pixel values froma single frame of image data.

[0045] Additional reader operating parameters can be determined byreading pixel values from a frame of image data clocked out according toa low resolution clock out mode of the invention. These additionalparameters which may be determined from a low resolution parameterdetermining frame of image data include an amplification parameter foradjusting the gain of an amplifier prior to analog-to-digitalconversion, an illumination level parameter for adjusting the currentlevel delivered to, and therefore the radiance of light emitted fromLEDs 22, an illumination time parameter for adjusting the on-time ofLEDs 22, a light level parameter for adjusting a light level of asubsequently captured frame of image data, a dark level parameter foradjusting a dark level, of a subsequently captured frame of image data,and an analog-to digital converter reference parameter for adjusting areference voltage of analog-to-digital converter 36.

[0046] While the present invention has been explained with reference tothe structure disclosed herein, it is not confined to the details setforth and this invention is intended to cover any modifications andchanges as may come within the scope of the following claims:

In the claims
 1. A method for operating an optical reader having animage sensor, said method comprising the steps of: clocking out at leastone frame of image data in a low resolution frame clock out mode ofoperation; reading pixel values from said at least one frame clocked-outin said low resolution clock out mode to determine an operatingparameter of said reader; and utilizing said operating parameter inoperating said reader.
 2. The method of claim 1, wherein said lowresolution mode clock out step includes the step of clock out electricalsignals corresponding to some pixel values of said image sensor at ahigher than normal clock out rate so that an overall frame clock outrate is increased.
 3. The method of claim 1, wherein said low resolutionmode clock out step includes the steps of clocking out some rows of saidimage sensor array at a normal clock out rate and other rows of saidimage sensor at a higher than normal clock out rate.
 4. The method ofclaim 1, wherein said low resolution clock out step includes the step ofselectively clocking out electrical signals corresponding to some pixelsof said image sensor and not clocking out electrical signalscorresponding to other pixels of said sensor.
 5. The method of claim 1,wherein said image sensor includes a discharge function actuated byactivation of a discharge control signals, wherein said low resolutionmode clock out step include the step of intermittently activating saiddischarge control signal while clocking out a frame of image data. 6.The method of claim 1, wherein said operating parameter is an exposureparameter value.
 7. The method of claim 1, wherein said operatingparameter is an illumination intensity value.
 8. The method of claim 1,wherein said operating parameter is an illumination on-time value. 9.The method of claim 1, wherein said operating parameter is an amplifiergain parameter value.
 10. The method of claim 1, wherein said operatingparameter is a dark level adjustment value.
 11. The method of claim 1,wherein said operating parameter is a light level adjustment value. 12.The method of claim 1, further comprising the step of decoding adecodable symbol representation represented in a frame of image datadeveloped utilizing said operating parameter.
 13. The method of claim 1,wherein said frame clocked out in said low resolution frame clock outmode is clocked out to produce a low resolution parameter determinationframe of image data in which valid and invalid data zones are defined byrows of said image sensor.
 14. The method of claim 1, wherein said imagesensor includes a one frame buffer and wherein said low resolution clockout step includes the step of clocking out three frames of image data ina low resolution frame clock out mode.
 15. A method for operating anoptical reader having an image sensor, said method comprising the stepsof: switching operation of said reader to a low resolution mode ofoperation; and in said low resolution mode, clocking out electricalsignals corresponding to some pixel values of said image sensor at ahigher than normal clock out rate so that an overall frame clock outrate is increased.
 16. The method of claim 15, wherein said clock outstep includes the steps of clock out some rows of said image sensorarray at a normal clock out rate and other rows of said image sensor ata higher than normal clock out rate.
 17. The method of claim 15, whereinsaid image sensor includes a discharge function actuated by activationof a discharge control signals, wherein said clock out step include thestep of intermittently activating said discharge control signal whileclock out a frame of image data.
 18. A method for operating an opticalreader having an image sensor, said method comprising the steps of:switching operation of said reader to a low resolution mode ofoperation; and selecting in said low resolution mode, clocking outelectrical signals corresponding to some pixels of said image sensor andnot clocking out electrical signals corresponding to other pixels ofsaid image sensor.
 19. An optical reader comprising: an imaging assemblyhaving an image sensor; a controller, wherein said controller is adaptedto clock out at least one low resolution frame of image data, whereinsaid controller is adapted to read pixel values from said at least onelow resolution frame of image data to determine an operating parameterof said reader, and wherein said controller is adapted to utilize saidoperating parameter in operating said reader.
 20. The reader of claim19, wherein said controller develops said low resolution frame of imagedata by clocking out electrical signals of said frame at a higher thannormal rate.
 21. The reader of claim 19, wherein said controllerdevelops said low resolution frame of image data by not clocking outelectrical signals corresponding to some pixels of said frame.
 22. Thereader of claim 19, wherein said operating parameter is an exposureparameter value.
 23. The method of claim 19, wherein said operatingparameter is an illumination intensity value.
 24. The method of claim19, wherein said operating parameter is an illumination on-time value.25. The method of claim 19, wherein said operating parameter is anamplifier gain parameter value.
 26. The method of claim 19, wherein saidoperating parameter is a dark level adjustment value.
 27. The method ofclaim 19, wherein said operating parameter is a light level adjustmentvalue.
 28. The reader of claim 19, wherein said controller is furtheradapted to decode a decodable symbol representation represented in aframe of image data developed utilizing said operating parameter. 29.The reader of claim 19, wherein said imaging assembly includes anillumination assembly.
 30. The reader of claim 19, wherein saidillumination assembly includes white LEDs.